An Evaluation of Hydrated Lime and Predator Sunfish as a Combined Chemical-Biological Approach for Controlling Snails in Aquaculture Ponds

摘要

Aquatic snails are vectors for several species of digenetic trematodes which infest many commercially cultivated fish. Most research in methods of controlling snails in aquaculture ponds has centered on chemical solutions applied to pond margins and stocking of mollusk-eating fish. We sought to evaluate both methods separately and in tandem as a combination treatment for snails in research ponds under simulated commercial food fish production conditions. Hydrated lime (Ca[OH]2) slurry applied at a rate of 31.7 kg/30.5 m of linear shoreline in a 1 m-wide swath produced a 99% reduction in estimated snail densities. However, estimated snail densities in several ponds rebounded within two months of application. Ponds stocked with redear sunfish Lepomis microlophus and hybrid crosses of the redear sunfish and green sunfish L. cyanellus at 494 fish/ha experienced a gradual decline in snail densities over four months, resulting in a 95% overall reduction at the end of the trial period (4 months). Ponds treated with both hydrated lime and predator sunfish experienced an abrupt decrease in snail densities with a less appreciable rebound, relative to the hydrated lime treatment group. Low abundances of encysted trematodes in crop fish reared within the research ponds coincided with very low densities of ram’s horn snails Planorbella spp. Estimated Planorbella densities in the month of crop fish stocking were most strongly correlated to trematode abundance in crop fish. All three methods reduced snail densities relative to the control; if conducted properly, a combination of two treatments may produce a rapid reduction of snail densities and maintain low snail numbers over the growing season.